DAC's are widely used in the electronic industry. By way of example, many application specific integrated circuits (ASIC's) employ one or more DAC's of the type shown in FIG. 1 in which a string of serially connected resistors connected between two voltage supplies V.sub.DD and V.sub.SS has a tap provided at a selected point in the string, at R.sub.DX in the example, to provide a voltage of a certain fraction of the range between the two voltage supplies at V.sub.OUT. This simple arrangement has provided a relatively stable ratiometric output on the order of 1%. However, certain applications have tightened accuracy requirements and can no longer tolerate this level of DAC error. It has been estimated that the drift, thermal or temporal, of a 10 bit DAC can be 1-2 LSB (minimum step size) steps. The normalized magnitude, that is, the number of LSB steps, of this drift can be significantly larger for DAC's which span only a fraction of the supply range. Slight differences in impurity doping or in stress relief with change in temperature and over time can cause drift which will change the fractional output of a DAC.